KR100385843B1 - A method of preparing polyethylene wax with a low polydispersity index and its apparatus - Google Patents

Abstract

The present invention relates to a method and apparatus for producing polyethylene wax having a low polydispersity index by thermal decomposition of a polyethylene resin produced by a polymerization method, in particular within a relatively short time without precise temperature control under mild conditions (atmospheric pressure and low stirring speed) A method for producing polyethylene wax having a low polydispersity index. In the present invention, prior to heating the raw material to the pyrolysis reaction temperature, a method for producing polyethylene wax having a preheating step, in particular a preheating step using a stepwise heating method to increase the thermal conductivity of the raw material can be carried out more effectively An apparatus is provided.

Description

A method for producing polyethylene wax having a low polydispersity index and a device therefor {A METHOD OF PREPARING POLYETHYLENE WAX WITH A LOW POLYDISPERSITY INDEX AND ITS APPARATUS}

The present invention relates to a method for producing polyethylene wax, and more particularly, to a method and apparatus for producing polyethylene wax having a low polydispersity index by thermal decomposition of a polyethylene resin produced by a polymerization method.

The polydispersity index is a term used in the polymer field and means a weight average molecular weight (Mw) divided by a number average molecular weight (Mn) (Mw / Mn). Here, a weight average molecular weight and a number average molecular weight are the measurements determined by experiment. In general, most commercially available polymeric materials have a wide molecular weight distribution because of their different chain lengths and molecular weights, and their polydispersity index is about 10. As such, when the molecular weight distribution is large and the polydispersity index is increased, workability is remarkably degraded when manufactured by other products. Therefore, when the molecular weight distribution of the polymer is narrowed and the polydispersity index is lowered, a polymer material having excellent processing to other products is obtained.

Wax generally refers to a material that is a plastic solid at any temperature but becomes a low viscous liquid at elevated temperatures. Since wax is a plastic-like material, it is usually deformed under pressure even without heating. Waxes usually encompass species and functional groups having a wide range of molecular weights. Although some varieties of wax and synthetic wax are completely hydrocarbon-based, honeycombs (ie beeswax) have been a common substance for many centuries. Waxes can be broadly divided into natural waxes derived from plants such as gum trees, cotton, saturation, and insects (waxy), whales (horny), and minerals, and synthetic waxes produced from synthetic raw materials. Representative synthetic waxes produced from synthetic raw materials include polyethylene (PE wax) and polypropylene (PP wax). (Encyclopedia of Chemical Technology, Vol 24, HF Mark et al . Eds, John Wiley Sons, New York, p 456 -481)

Generally, there are a polymerization method and a pyrolysis method for producing polyethylene wax. The polymerization process involves the addition of a chain transfer agent (propane, butane, and the like) or hydrogen to the high temperature polymerization or low pressure medium pressure (using a Ziegler type catalyst) using an appropriate catalyst. It can be operated in a continuous process as a manufacturing method has the advantage that the mass production is possible and the molecular weight can be easily controlled, but the disadvantage of large equipment and large investment costs. U.S. Pat.Nos. 2,153,553, 2,188,465 and 2,219,684 are known for producing polyethylene waxes by polymerization of ethylene at at least 500 atmospheres and 100-400 ° C. with oxygen as the initiator. US Pat. No. 2,387,755 discloses that the production of polyethylene wax is carried out in the presence of hydrogen, while US Pat. No. 3,557,074 (1971.1.19) uses free radical initiators to increase the temperature (200-200 ° C.) and atmospheric pressure. Ethylene was polymerized at high pressure (1200-2500 atm, preferably 1200-1800 atm) to produce polyethylene wax with a softening point of 100-106 ° C and a melting temperature of 200-2000 cP. to discloses that are affected by the addition of the C ₃ ~C ₄ alkene of 0.5 to 3% (preferably 1 to 2%) with hydrogen or a C ₂ ~C ₄ alkanes and (b) volumes of 10 to 30% . The polymerization reaction in that process is affected by the free radical initiator. Traditional free radical initiators include oxygen, t-butyl peroxyacetate, dilauroyl peroxide, benzoyl peroxide, di-t-butyl peroxide and mixtures thereof.

U.S. Patent No. 3,567,703 (Mar. 3, 1971) describes a polyethylene wax having a molecular weight of 1000 to 3000 g mol ^-1 and a melting point of 100 to 125 ° C, which is a tertiary amine non-aromatic with nitrogen or chelate diamine. ) Was prepared by polymerization of ethylene at 101-150 ° C. using a catalyst prepared in combination. The products produced in this way have the use of paper coatings, floor polishes and the like, described in this patent document. The R group of the lithium component can be a radical of any hydrocarbon of a particular number of carbon atoms, including aliphatic, cycloaliphatic, aryl, alkaryl and alkenyl groups. Suitable R groups for the components of LiR include ethyl, propyl, isopropyl, n-butyl, t-butyl, n-amyl, iso-amyl, n- or isooctyl, n- or isodecyl, lauryl, Cyclopentyl, methylcyclonuclear, phenyl, benzyl, tolyl, xylyl, cumyl, methylbenzyl, propylbenzyl, 2-phenylethyl, allyl, crotonyl and the like. LiR is preferably alkyl lithium having an alkyl group having 2 to 10 carbon atoms.

Pyrolysis of PE, on the other hand, occurs clearly at the chain branching point of the polymer. Careful control of time, temperature, and agitation yields pyrolyzed PE, which has a relatively narrow molecular weight than unmodified high molecular weight PE. Pyrolysis reaction is performed at the temperature of about 290 degreeC-about 425 degreeC. The pyrolysis reaction is carried out in the absence of air or other oxidants, possibly during stirring in a vacuum or pressure bath. The process known in US Pat. No. 3,441,628 (1969.4.29) consists in conducting heat while passing high molecular weight PE through a small diameter tube where pyrolysis occurs at a temperature of 100-300 ° C. and a pressure of 140-420 atmospheres.

All processes in which low molecular weight PEs, such as waxes obtained by pyrolysis, are produced have the disadvantage that the pyrolysis reaction is not complete or in some sense overheated due to the low thermal conductivity of the products such as PE and the wax produced. Such drawbacks hinder the production of products with uniform molecular weight. One way to overcome this disadvantage is to carry out the pyrolysis reaction in a suitable heat resistant solvent. When using low boiling solvents such as nucleic acids, the reaction should be carried out under pressure to avoid evaporation of the solvent. It is therefore desirable to use solvents with higher boiling points, such as liquid paraffin, for pyrolysis reactions. However, they cause problems in subsequent solvent removal due to the chemical similarity between paraffins and pyrolysis products, and therefore, considerably costly.

Pyrolysis reactions depend on temperature and residence time. However, when a constant temperature is maintained, the decomposition curve shows a break for some time period. Using these results, U.S. Pat. Or a molecular weight modifier is introduced into the initial product before or during the decomposition process in a known manner, respectively, and a high molecular weight ethylene polymer and copolymer, such as plastic, in the absence of air or oxygen, is preferably Is a prepared melt of partially decomposed ethylene polymer (polymer) and copolymer during dwell time (preferably 2 to 5 minutes) from 30 seconds to 5 hours at 360-420 ° C. Pyrolysis into the core to produce low molecular weight, virtually linear ethylene polymers, such as wax It was developed. They can make a mixture of high molecular weight polymer and low molecular weight polymer at room temperature and then melt the mixture to bring it to the desired temperature, or put the ethylene polymer to be decomposed into the melt of low molecular weight polymer below the decomposition temperature and subsequently decompose the two components. It is also reported that a high molecular weight polymer in a molten state can be added into a melt of a low molecular weight polymer which is heated to or at a decomposition temperature or heated to a decomposition temperature after addition of the high molecular weight polymer. Examples of radical generating agents are oxygen, peroxides such as lauroyl peroxide, benzoyl peroxide, di-t-butyl peroxide and t-butyl-perbenzoate, and azo compounds, i.e., αα'-azo-bisbutyro -Nitrile. Further examples of molecular weight modifiers include propane, high molecular weight paraffins, hydrogen and cyclohexane.

In addition, Shin Dong-geun has a high pressure of 20㎏ / ㎠ and a relatively rapid stirring at 1,000 rpm, and has a melt flow index of 10.0, a density of 0.923, a tensile strength of 110㎏ / ㎠, and a number average molecular weight in a high pressure reactor. 2 kg of this 9,931 polyethylene resin was pyrolyzed at a reaction temperature of 360 to 390 ° C. for 1 to 3 hours to prepare polyethylene wax having a number average molecular weight of 1,588 to 4,980 g / mol and a polydispersity index of 1.62 to 3.58. , Young-Chul Kim, Se-Moon Shim, Je-Hwan Choi, "Study on the manufacture of medium molecular weight polyethylene wax", Ministry of Science and Technology, 1983)

In Japanese Patent Laid-Open No. 3-62804, a pressure of 0.2 to 20 kg / cm 2 is used by using two or more series-connected tubular reactors (length of 5 to 100 m) with or without a static mixer. Low molecular polyethylene having a number average molecular weight of 500 to 10,000 g / mol was continuously produced by thermally decomposing the polyethylene resin in a linear speed of 5 to 100 m / hr, a reaction temperature of 300 to 450 ° C., and an inert gas for 0.5 to 10 hours.

Rice and Cosiakov argued that the "cage effect" due to the slow diffusion of radicals caused "long chain branching." Carbon-carbon bonds of the most sensitive (ie allyl bonds present in the resin) of the points (BD, 335 kJ mol ^-1 ) branched by a bond dissociation energy (BDE) of 257 kJ mol ^-1 The release of radicals by the intermolecular reaction following the initiation step leading to the break of is favorable to the radicals in the molecule. Thus, propagation steps and termination reactions are controlled by diffusion in the viscous solution. A simple way to minimize this is to dilute the solution with a solvent (Rice, FO and Kossiakoff, A, J, Am. Chem. Soc. , 65, 590, 1943). Roasting and Pari were subjected to batch pyrolysis of HDPE in dilute solution to obtain a wax product with a number average molecular weight of 2000-6000 gmol ^-1 . Dilution with phenyl ether in typical volumetric pyrolysis (390 ° C., 6 h), which gives branched wax polymers, is characterized by the product's properties (low molecular weight, narrow distribution, high crystallinity, abundant α-olefin and small amount of long branches). To control the diffusion reaction). (Guy, L. and B. Fixari, "Waxy Polyethylenes from Solution Thermolysis of High Density Polyethylene: Inert and H-doner solvent Dilution Effect", Polymer , 40, 2845-2857, 1999)

Research has also been carried out to produce useful chemicals and oils, including waxes, through thermal and catalytic cracking of waste plastics. Woodin et al. Used four different types of PE, so-called high-density PE (HDPE), low-density PE (LDPE), linear low-density PE (LLDPE) to produce useful chemicals and oils through thermal and catalytic decomposition of waste PE resins. The crosslinked PE (XLPE) was thermally decomposed batchwise at 430 ° C. using silica-alumina as the solid acid catalyst or without any catalyst. In the case of pyrolysis, HDPE and XLPE produced significant amounts of wax-like components because the structure of the polymer being degraded affects the yield of the product, and the yield of liquid products (58-63 wt%) was LDPE and LLDPE (76-77). It was reported that the yield was lower than the wt%) and LDPE and LLDPE produced very small amounts of wax-like components (Uddin, MA, K. Koizumi, K. Murata and Y. Sakata, "Thermal and Catalytic Degradation of Structurally Different"). Types of Polyethylene into Fuel Oil ", Polymer Degradation Stability , 56, 37-44, 1997)

Murti et al also evaluated the effect of polymer filler on pyrolysis of HDPE to produce liquid raw materials. They were thermally decomposed to HDPE in the presence or absence of a metal additive _{(Al (OH) 3 · xH} 2 O, AlCl 3, Al 2 O 3, CaCO 3, CuO, ZrO 2, Fe 2 O 3), of Al ₂ O ₃ The use delayed the liquefaction of HDPE, resulted in the formation of waxes, and in the noncatalytic pyrolysis of PE, most of the products were reported to be waxes with a liquid yield of less than 5% (Murty, MVS, EA Grulke and D. Bhattacharyya, "Influence of Metallic Additives on Thermal Degradation and Liquefaction of High Density Polyethylene (HDPE)", Polymer Degradation Stability , 61, 421-430, 1998)

As described above, the polymerization method of the plurality of polyethylene waxes can be operated in a continuous process, so that mass production is possible and the molecular weight can be easily controlled, but there are disadvantages in that the size of the apparatus and the investment cost are large.

In the conventional pyrolysis method, a polyethylene wax is generally produced by thermally decomposing polyethylene resin in a stirred tank reactor or a tubular reactor at a constant reaction temperature at a time, but the conventional thermal decomposition method is used because the thermal conductivity of polyethylene resin is low. In order to produce polyethylene wax having a low polydispersity index, it is necessary to maintain a high pressure, rotate the stirrer at a high speed, adjust the temperature of the raw material very precisely, or increase the manufacturing time.

The method of carrying out the pyrolysis reaction in the heat resistant solvent causes a problem in subsequent solvent removal due to the chemical similarity between the heat resistant solvent used and the product of the pyrolysis reaction, and therefore, there is a problem that considerable cost is required. .

Accordingly, the present invention has been made to solve the problems of the prior art, and in the present invention, polyethylene wax having a low polydispersity index can be produced in a relatively short time without precise temperature control under mild conditions (atmospheric pressure and low stirring speed). It aims to provide a way to.

In addition, an object of the present invention is to provide an apparatus that can more effectively perform the manufacturing process of the polyethylene wax.

1 schematically shows an external circulation loop reactor in which two tubes are installed perpendicular to the reactor.

FIG. 2 shows the loop reactor of FIG. 1 in three dimensions.

3 shows an external circulation loop reactor in which three vertical tubes are installed.

Figure 4 shows a longitudinal cross-sectional view of the inner loop loop reactor is installed inside the draft tube (draft tube).

5A-5C are enlarged views of the impeller shown in FIGS. 1 and 4 and shown at various angles.

<Description of the symbols for the main parts of the drawings>

1: gas discharge valve 2: heat exchanger

3: raw material inlet 5: stirring motor

6: inert gas injection valve 7: vertical pipe

7a: riser 7b: downcomer

8: upper connector 9: lower connector

10: thermocouple 14: axis of rotation

16: reactor outer wall 21: draft tube

22: heating part 23: insulating part

30 impeller 31: circular flow generating wing

32: wall scraping wing 33: radial flow wing

In order to achieve the above object, in the present invention, a method for producing polyethylene wax having a preheating step, in particular a preheating step using a stepwise heating method in order to increase the thermal conductivity of the raw material before heating the raw material to the pyrolysis reaction temperature. To provide.

That is, the method for producing polyethylene wax according to the present invention is a method for producing polyethylene wax having a number average molecular weight of 500 to 10,000 by thermally decomposing polyethylene resin in an inert gas atmosphere, and heating the polyethylene resin as a raw material to a thermal decomposition reaction temperature. Prior to this, in order to increase the thermal conductivity of the raw material, a preliminary temperature of 110 ° to 390 ° C. increases the temperature of the surface of the raw material or the reactor to a constant temperature above the melting point of the raw material to maintain the raw material at a time sufficient to reach a uniform state as a whole. It is characterized by having a heating step.

In particular, the pre-heating step in the manufacturing process of the polyethylene wax, preferably a stepwise heating method having a repetitive process of increasing the temperature again to reach a uniform state when the raw material reaches a uniform state to reach a uniform state In addition, the manufacturing method is more preferably carried out using a loop reactor using all of the outer wall of the circulation pipe through which the raw material is circulated as a heating surface.

In the above production process, in order to achieve a more uniform reaction and a shorter reaction time, the heat transfer rate from the heated wall surface to the raw material must be fast and the raw materials must be effectively mixed well. At this time, the heat transfer rate is proportional to the temperature difference and the heat transfer area between the materials to exchange heat, so increasing the heat transfer area per unit volume of the raw material can reduce the reaction time. The pyrolysis reactor generally used in general is a stirred tank reactor, and heats the outer wall of the reactor to supply the amount of heat required for the reaction, so the heat transfer area becomes the surface area of the outer wall where the heater is installed. Therefore, when using a loop reactor that can use all the outer wall of the tube circulating the raw material as a heating surface instead of the stirring vessel reactor can increase the heat transfer area per unit volume of the raw material can significantly shorten the manufacturing time.

In addition, the present invention provides a device that can more effectively perform the manufacturing process of the polyethylene wax of the present invention. The apparatus according to the present invention is a raw material input unit for inputting the raw material, a gas injection unit for injecting inert gas into the reactor, a stirring unit for stirring the raw material, a heating unit for heating the outer wall of the reactor, to measure and adjust the temperature of the raw material In the pyrolysis reactor for manufacturing a wax equipped with a thermocouple and a product discharge part for discharging the finished wax, a circulation pipe for circulating the raw material is installed in the reactor and the outer wall of the circulation pipe as a loop reactor using all the heating surfaces The inside of the circulation flow generating blades are installed at an angle to each other in a direction perpendicular to the axis of rotation alternately diagonally; A wall scraping wing attached obliquely to one end of said circular flow generating wing; An impeller made of a radially mixed blade attached to the other middle portion of the circular flow generating blade in the rotational axis direction is provided.

In one embodiment of the present invention, in one form of the loop reactor, two or more vertical tubes 7 and upper connecting tubes 8 connecting upper portions of the vertical tubes and a lower portion of the vertical tubes are connected to the circulation tube. To provide an outer circulation loop reactor consisting of a lower connecting pipe (8).

In another embodiment of the present invention, there is provided an internal circulation loop reactor in which a draft tube in which a heater is built in the reactor is installed.

Hereinafter, a method for preparing polyethylene wax having a low polydispersity index according to the present invention will be described in detail.

The process for producing polyethylene wax according to the present invention can be divided into raw material input step, preheating step, reaction step and cooling step.

(1) Raw material input stage

The raw material is introduced into the reactor, and the inside of the reactor is made into an inert gas atmosphere by filling the reactor internal space with an inert gas (for example, nitrogen) at a pressure higher than atmospheric pressure.

(2) preheating stage

In order to increase the thermal conductivity of the raw material, the wall temperature of the raw material or the reactor is raised to a constant temperature above the melting point of the raw material within the range of 110 to 390 ° C., and maintained at a sufficient time for the raw material to reach an overall uniform state. Preferably, when the raw material reaches a uniform state, a stepwise heating method having one or more repetitive processes of increasing the temperature again to reach a uniform state is used.

The temperature and time of the preheating stage vary depending on the condition and the quantity of the raw material. In general, a constant temperature is set above the melting point within the temperature range of 110 to 390 ° C. and maintained until the raw material reaches a uniform state. . At this time, it is preferable to maintain the set temperature in the range of ± 10 ° C. The temperature setting as described above is such that the temperature is 110 ° C or more, which is equal to or higher than the melting point of the polyethylene resin as the raw material, and 390 ° C or less, which is a temperature before full thermal decomposition reaction occurs. Therefore, the temperature of this preheating step is usually lower than the temperature of the reaction step, and includes a low reaction temperature at which the relatively pyrolysis reaction is slow.

Using a stepwise heating method in which the preheating process is repeated several times while increasing the temperature increases the manufacturing time required compared to the case of preheating only once, but enables the production of polyethylene wax having a lower molecular weight distribution. Therefore, the number of repetitions of the preheating process is appropriately adjusted in consideration of the time required for the overall manufacturing process and the desired molecular weight distribution.

(3) reaction step

After the preheating step, the temperature of the raw material is raised to the reaction temperature (generally, 300 to 450 ° C.) and pyrolyzed for 0.4 to 10 hours until the desired product is produced while controlling the temperature of the raw material to ± 2 ° C. The reaction time depends on the reaction temperature, the amount of raw material and the value of the desired product viscosity or number average molecular weight.

(4) cooling stage

After the pyrolysis reaction, cool the product until the temperature reaches about 350 ℃ or less.

The manufacturing process of the present invention as described above can be carried out more effectively by using a loop reactor instead of the conventional stirred tank reactor.

The loop reactor uses all the outer walls of the circulation pipe where the raw material is circulated as a heating surface, thereby increasing the heat transfer area per unit volume of the raw material and greatly shortening the reaction time. In the present invention, a tube through which raw materials are circulated in all types of loop reactors (for example, a vertical tube and its connecting tube, a draft tube and its external circulation portion, etc.) is collectively referred to as a "circulating tube".

In addition, in the present invention, in order to improve the production efficiency of wax, a separate loop reactor suitable as a pyrolysis reactor for preparing wax is used separately.

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment of the loop reactor for producing wax according to the present invention. However, the wax production method according to the present invention is not limited to the loop reactor of the type described below, and may be performed by other types of loop reactors as well as conventional stirred tank reactors.

FIG. 1 shows an external circulation loop reactor in which two tubes are installed perpendicular to the reactor, and FIG. 2 shows the loop reactor of FIG. 1 in three dimensions.

This outer circulation loop reactor uses two vertically installed pipes and the outer wall of the upper and lower connection portions connecting them to the heating surface, thereby greatly improving the heat transfer area per unit volume of the raw material, compared to the conventional agitator reactor. As a result, the reaction time is dramatically shortened.

The reactor is a basic configuration of a pyrolysis reactor for wax production, a gas discharge valve (1) for discharging an inert gas (for example, nitrogen) during purging, and a material having a low breaking point among volatile substances generated during the reaction. Heat exchanger (2) for condensing and returning to the reactor, raw material inlet (3) into which polyethylene resin is introduced, and the ability to absorb and remove water soluble substances from the volatile substances passing through the heat exchanger from the exhaust gas and condensation in the heat exchanger A gas absorption tank 4, which collects low-molecular weight wax that does not come out, a stirring motor 5 for stirring raw materials, and an inert gas (for example, nitrogen gas) to remove oxygen from the air in the reactor Valve (6) for injecting, thermocouple (10) for measuring and adjusting temperature, sampling valve (12) and valve (13) for discharging product, reaction The provided with a heater or the like installed on the outer wall 16 of the outside or the reactor.

The outer circulation loop reactor of the present invention shown in Figs. 1 to 3 has two or more vertical pipes 7, ie, a rising pipe 7a and a lower pipe installed vertically in the pipe in the basic configuration as the pyrolysis reactor as described above. Steel pipe (7b) and the upper connecting pipe (8) connecting them, the lower connecting pipe (9), and the impeller 30 for uniform stirring and the rotating shaft 14 for rotating it. Detailed description of the impeller 30 will be described later.

The loop reactor is provided with a heater (not shown) in the circulation pipe, that is, the rising pipe 7a, the down pipe 7b, and the upper connection pipe 8 and the lower connection pipe 9 connecting them, All outer walls are used as heating surfaces.

As the heater, all available heating means (for example, coil, plate, various types of heaters, gas heaters, etc.) can be used, and the temperature of the raw material or the wall surface of the reactor is controlled by controlling the heat amount of the heating means with a controller. Done. For example, in the case of using the electric heating means, the raw material or the wall temperature is controlled by controlling the voltage supplied to the heater using the controller.

As the material of the circulation pipe, that is, the rising pipe 7a, the falling pipe 7b, the upper connecting pipe 8 and the lower connecting pipe 9, a material that can withstand the pyrolysis reaction temperature and has excellent thermal conductivity (for example, , Stainless steel, etc.).

Thermocouples are installed inside and on the walls of certain parts of the circulation pipe (for example, riser pipes) to measure and adjust the temperature of the raw material and the temperature of the outer wall.

3 is an external circulation loop reactor in which three vertical pipes 7 through which raw materials are circulated are installed. In the external circulation loop reactor of the present invention, the number of vertical tubes through which the raw material is circulated can be increased to three or more, but as the number of vertical tubes increases, the heating surface is increased accordingly, thereby improving heat transfer performance.

Figure 4 shows a longitudinal cross-sectional view of an internal circulation loop reactor having a draft tube installed therein.

The basic configuration of the inner circulation loop reactor is the same as the outer circulation type except that the draft tube 21 having the heating unit 22 built therein is installed in the reactor instead of the vertical tube. At this time, the same heating unit 22 is also installed on the outer wall 16 of the reactor, so that the outer wall of the pipe through which the raw material is circulated is used as the heating surface.

Like the external circulation loop reactor, the heating unit 22 may use all available heating means (for example, various types of heaters such as coils and plates, gas heaters, and the like). When electrical means are used as the heating means, the outside of the heating part is surrounded by the insulating part 23. The material of the outer wall 24 surrounding the heating part or the insulating part is the same as the description of the material of the vertical tube of the outer circulation loop reactor described above.

5 shows an impeller used in a loop reactor of the present invention.

The impeller improves radial mixing and promotes circulation of the raw materials contained in the loop reactor. The impeller includes a circular flow generating blade 31, a wall scraping blade 32, and a radial mixing blade 33.

The circulation flow generating blades 31 are installed at an angle to each other at right angles to the rotation shaft 10 at an angle to each other to generate a rising or falling circulation flow. That is, when the rotating shaft rotates counterclockwise, the circular flow generating blade 31 generates a rising flow, and when the rotating shaft rotates clockwise, a descending flow is generated. You get a directional mix.

Wall scraping blades 32 and radially mixed blades 33 are attached to the left and right sides of the circular flow generating blades, respectively. The wall scraping blade 32 attached obliquely (about 45 °) to one end of the circular flow generating blade 31 serves to scrape the raw material close to the wall and move it toward the rotation axis, and the other side of the circular flow generating blade 31. The radial mixing blade 33 located in the direction of the rotation axis in the middle portion serves to move the raw material near the rotation axis toward the wall to improve the radial mixing.

In the loop reactor of the present invention, a plurality of such impellers are installed on the rotating shaft 10 inside the circulation pipe, so that the rising shaft 7a rotates the rotating shaft counterclockwise so that the rising flow occurs, and the falling pipe 7b descends the flow. Turn clockwise to get this.

Hereinafter, a process for preparing polyethylene wax having a low polydispersity index according to the present invention using an external circulation loop reactor shown in FIG. 1 will be described by the following preferred embodiment.

First, the raw material inlet 3 is opened, and the polyethylene resin is introduced into the loop reactor. Several times, the inside of the reactor is filled with an inert gas at a pressure higher than atmospheric pressure and then removed to make oxygen in the reactor into an inert atmosphere. In order to increase the number of heat transfer of the raw material, the temperature of the controller is set above the melting point of the raw material in one or more preheating steps, and then all the heaters installed in the circulation pipes 7a, 7b, 8, and 9 are operated to heat the reactor. The temperature of raw material is controlled and maintained at the set temperature ± 10 ℃ for more than 1 minute. After the pre-heating step, set the controller's set temperature to the reaction temperature (300 ~ 450 ℃) to increase the temperature of the raw material and control the temperature of the raw material to the reaction temperature ± 2 ℃ until the desired product is made. Pyrolyze for a certain time (0.5 to 10 hours). The specific reaction time depends on the reaction temperature, the amount of raw material and the value of the desired product viscosity or number average molecular weight. After the reaction, the heaters are all turned off and cooled until the temperature of the product reaches approximately 350 ℃ or less. The cooled product is discharged through the product discharge valve 13 installed in the lower part of the reactor. In the preheating step and the reaction step, the raw materials and reactants contained in the reactor are suitably stirred by rotating the impeller 30 which generates radial mixing and circulation flow. The total time taken to produce the desired polyethylene wax is determined by the reaction temperature described above, the amount of raw material, the viscosity or number average molecular weight of the desired product, as well as the number of preheating steps and the maximum voltage (or maximum heating amount) supplied to the heater. Depends on.

Hereinafter, the production method of the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the scope of the present invention is not limited by the following examples, and in particular, the method of the present invention is not limited to the following reactors, but may be performed by other types of loop reactors as well as conventional stirred tank reactors.

Example 1

2 kg of polyethylene resin having a density of 0.924 g / cm 3, a melting point of 110 ° C., a number average molecular weight of about 23,000 g / mol, and a polydispersity index of about 7.44 was introduced into the external circulation loop reactor of FIG. 1. Close the exhaust gas discharge valve (1), open the nitrogen injection valve (6) and inject with 2 atm of nitrogen, close the nitrogen gas injection valve, open the exhaust gas discharge valve, and discharge the nitrogen eight times. Oxygen in the air in the reactor was removed. The maximum voltage supplied to the heater was all set at 200V. The controller was set at 370 ° C. for 40 minutes while controlling the temperature of the raw material to 370 ± 6 ° C. in the preheating step. In the reaction step, the set temperature of the controller was set to 390 ° C. to increase the temperature of the raw material, and pyrolyzed the raw material for 75 minutes while maintaining the temperature at 390 ± 1 ° C. During the operation, when the temperature of the raw material reaches 120 ℃, the stirrer is increased to 20rpm, and when it reaches 250 ℃, the stirrer is increased to 20rpm. After that, the rotational speed is increased by 20rpm every 5 minutes until the stirrer rotates to 120rpm. To obtain polyethylene wax. The preparation time including the reaction step was 3 hours and 15 minutes. The experimental results for the obtained product are shown in Table 1.

Example 2

The same procedure as in Example 1 was conducted except for the following. Set the controller's set temperature to 330 ℃, maintain the temperature of the raw material to 330 ± 9 ℃ for 50 minutes in the preheating stage, and set the set temperature of the controller to 400 ℃ in the reaction stage to raise the raw material temperature to 400 ±. The raw material was pyrolyzed for 25 minutes while maintaining at 2 ° C to obtain polyethylene wax. The preparation time including the reaction step was 2 hours 25 minutes. The experimental results for the obtained product are shown in Table 1.

Example 3

The same procedure as in Example 1 was conducted except for the following. For the preheating of raw materials, the controller's set temperature is first set to 250 ℃, and when the temperature of the raw material reaches the corresponding temperature for the first time, it waits for 1 hour, after which the controller's set temperature is increased by 20 ℃ and the temperature of raw materials increases. When the set temperature was reached, the preheating process of waiting for 1 hour was repeated seven times until the set temperature reached 370 ° C. In the reaction step, the controller was set at 390 ° C. to raise the temperature of the raw material and thermally decompose the raw material for 68 minutes while maintaining the temperature at 390 ± 4 ° C. to obtain polyethylene wax. The preparation time including the reaction step was 9 hours 33 minutes. The experimental results for the obtained product are shown in Table 1.

Comparative Example 1

The process was carried out in the same manner as in Example 1, except that the raw material was pyrolyzed for 83 minutes by setting the set temperature of the controller to 390 ° C. without preliminary heating. The preparation time including the reaction step took 2 hours and 27 minutes. The experimental results for the obtained product are shown in Table 1.

Viscosity (Unit cP) * Number average molecular weight (g / mol) Polydispersity Index Preheating Process Example 1 342 3821 3.58 One Example 2 295 3550 3.62 One Example 3 288 4312 3.66 7 Comparative Example 1 344 2508 9.23 0 * Measured at 140 ℃

As can be seen from the results of the above examples and comparative examples, according to the production method of the present invention, polyethylene wax having a low polydispersity index can be produced without using precise temperature control or a large-capacity stirring motor and high pressure equipment. In addition, industrial scale production can be efficiently performed.

Polyethylene waxes obtained in the present invention are used in industrial applications such as the manufacture of hot melt adhesives, plastic processing aids, antislips, antimars, rubber additives, ink additives, varnishes, cosmetics and paper coatings. Can be used for purposes.

Claims (6)

In the method for producing a polyethylene wax having a number average molecular weight of 500 to 10,000 by thermally decomposing the polyethylene resin in an inert gas atmosphere, Prior to heating the polyethylene resin as a raw material to the pyrolysis reaction temperature, the wall temperature of the raw material or the reactor is raised to a certain temperature above the melting point of the raw material within the range of 110 to 390 ° C. to increase the thermal conductivity of the raw material. A process for producing polyethylene wax having a low polydispersity index, characterized in that it has a preheating step that is maintained at a time sufficient to reach a state. The method of claim 1, The preliminary heating step, characterized in that using a stepped heating method having a repetitive process of increasing the temperature to reach a uniform state by increasing the temperature again when the raw material reaches a uniform state. The method of claim 1, The method is characterized in that it is carried out using a loop reactor using all of the outer wall of the circulation pipe circulating the raw material as a heating surface. Raw material input part for inputting raw material, gas injection part for injecting inert gas into reactor, stirring part for stirring raw material, heating part for heating outer wall of reactor, thermocouple and finished wax for measuring and controlling the temperature of raw material In the pyrolysis reactor for manufacturing a wax provided with a product discharge part for discharging, A loop reactor in which a raw material is circulated in the reactor and the outer wall of the circulation pipe is used as a heating surface, the inside of the circulation pipe having circulating flow vane installed at an angle to each other in a direction perpendicular to the rotation axis; A wall scraping wing attached obliquely to one end of said circular flow generating wing; Loop reactor for producing polyethylene wax, characterized in that the impeller consisting of a radial mixing blade attached in the direction of the rotation axis in the other middle portion of the circulation flow generating blades. The method of claim 4, wherein The circulation pipe consists of at least two vertical pipes (7), an upper connection pipe (8) connecting the upper portions of the vertical pipes, and an external circulation pipe, characterized in that the lower connection pipes (8) connect the lower portions of the vertical pipes. Type loop reactor. The method of claim 4, wherein The circulation pipe is an internal circulation loop reactor, characterized in that the draft tube with a heater is installed inside the reactor.